Paraffin conversion

ABSTRACT

A process for disproportionating feed light alkane to obtain higher molecular weight hydrocarbons which comprises contacting the feed light alkane, at elevated temperature and pressure, with a catalyst comprising a molecular sieve composited with a Group VIII noble metal. Preferably the contacting is carried out in the presence of H2O.

United States Patent Mulaskey [54] PARAFFIN CONVERSION [72] Inventor:Bernard F. Mulaskey, Fairfax, Calif.

[73] Assignee: Chevron Research Company, San Francisco, Calif.

[22] Filed: Apr. 17, 1970 [21] Appl. No.: 29,701

[52] US. CL. ..260/676 [5 1 Int. Cl ..C07c 9/00 [58] Field of Search..260/676, 683 D, 673.5;

[56] References Cited UNITED STATES PATENTS I 3,247,099 4/1966 Oleck..208/ 138 3,369,997 2/1968 Hayes et al. 3,51 1,773 5/1970 Addison etal. 3,544,648 12/1970 Wilson et a1...

3,546,314 12/1970 Larson .:::.260/683D 1 lune 6, 1972 PrimaryExqminer-Delbert E. Gantz Assistant Examiner-J. M. Nelson I Attorney-A.L. Snow, F. E. Johnston, G. F. Magdeburger, C. J. Tonkin and T. G. DeJonghe ABSTRACT A process for disproportionating feed light alkane toobtain higher molecular weight hydrocarbons which comprises contactingthe feed light alkane, at elevated temperature and pressure, with acatalyst cornprising a molecular sieve composited with a Group VIIInoble metal. Preferably the contacting is carried out in the presence ofH 0.

8 Clain is, No Drawings PARAFFIN CONVERSION BACKGROUND OF THEINVENTION 1. Field of the Invention The present invention relates to theconversion of alkane hydrocarbon feeds to hydrocarbon products withdifferent distributions of molecular weights than those of the feeds.More particularly, the present invention relates to thedisproportionation of alkane hydrocarbons, in the presence of H 0, usinga catalyst comprising a molecular sieve composited with a Group VIIInoble metal.

The term disproportionation is used herein to mean the conversion ofhydrocarbons to new hydrocarbons of both higher and lower molecularweight. For example, propane may be disproportionated according to thereaction:

first cracked to form substantial amounts of olefins. Then the olefinsare polymerized to higher-boiling compounds by contacting the olefinswith a catalyst adapted to promote the forming of heavier hydrocarbonsby polymerization.

U.S. Pat. No. 1,687,890 is directed to a process of convertinglow-boiling point hydrocarbons into higher-boiling point hydrocarbons bymixing a hydrocarbon vapor with steam and then contacting thesteam-hydrocarbon mixture with iron oxide at temperatures in excess of1,1 12 F.-It is theorized in U.S. Pat. No. 1,687,890 that the followingreactions may be involved to a greater or lesser extent:

1. Paraffin hydrocarbons on being brought into contact with ferric oxideat elevated temperatures are oxidized or dehydrogenated, formingunsaturated hydrocarbons.

2. Unsaturated hydrocarbons of low molecular weight polymerize intounsaturated hydrocarbons of higher molecular weight when subjected toelevated temperatures, the extent of polymerization depending upon thetemperature and duration of treatment.

3. Ethylene and other gaseous hydrocarbons, including methane, reactwith ferric oxide at temperatures of from 500 to 550 C. forming ferrousoxide, water and carbon.

4. Carbon reduces ferric oxide to ferrous oxide at temperatures of from550 to 600 C. with production of carbon monoxide.

5. Carbon monoxide reduces ferric oxide to ferrous oxide at temperaturesof from 550 to 600 C. with formation of carbon dioxide.

6. Water vapor reacts with ferrous oxide at about 600 C.

forming ferric oxide and highly reactive or so-called nascent hydrogen.

7. Unsaturated hydrocarbons are hydrogenated by nascent hydrogen."

Another process which has been proposed for converting hydrocarbons tohigher molecular weight hydrocarbons is olefin disproportionation.Numerous methods and catalysts have been disclosed for thedisproportionation of olefins. In most of these processes, the olefin isdisproportionated by contacting with a catalyst such as tungsten oxideor molybdenum oxide on silica or alumina at a temperature between about150 and 1,110 F. and at a pressure between about 15 and 1,500 psig.These prior art processes have been directed to an effective method toconvert essentially only olefins, not

alkane hydrocarbons, to higher molecular weight hydrocarbons bydisproportionation.

For example, in U.S. Pat. No. 3,431,316, an olefin disproportionationprocess is disclosed, and it is stated that, if desired, paraffinic andcycloparaffinic hydrocarbons having up to 12 carbon atoms per moleculecan be employed as dilutents for the reaction; that is, the alkanehydrocarbons are nonreactive and merely dilute the olefins which are thereactants.

A process for the direct conversion of alkane hydrocarbons to highermolecular weight hydrocarbons would be very attractive because in manyinstances alkane hydrocarbons are available as a relatively cheapfeedstock. For example, in many instances, excess amounts of propaneand/or butanes are available in an overall refinery operation.

Processes which have been previously reported wherein alkanehydrocarbons are disproportionated include contact of alkanehydrocarbons with solid catalyst comprised of AlCl on A1 0 and contactof alkane hydrocarbons with a promoter comprised of alkyl fluoride andBF,. The use of the AlCIl solid catalyst was uneconomic because, amongother reasons, the catalyst was nonregenerable. The use of the alkylfluoride and BE, was unattractive because of severe corrosion, sludgeformation and other operating problems.

In the past it has been the practice to convert alkane hydrocarbons,particularly normal alkanes, to olefins as a separate or distinct stepand then to disproportionate the olefins to valuable higher molecularweight hydrocarbons.

For example, in U.S. Pat. No. 3,431,316, saturated light hydrocarbonsare cracked to form olefins, and then the olefins are separated from thecracker effluent and fed to a disproportionation zone wherein theolefins are disproportionated to higher molecular weight hydrocarbons.Thus, a separate step is used to obtain olefins, because, according tothe prior art, no economically feasible process is available for thedirect disproportionation of alkane hydrocarbons.

U.S. Pat. No. 3,445,541 discloses a process for thedehydrogenation-disproportionation of olefins and paraffins using acombined dehydrogenation and disproportionation catalyst. According toU.S. Pat. No. 3,445,541, a hydrocarbon feed which is either an acyclicparaffin or acyclic olefin having three to six carbon atoms is contactedwith the catalyst at conditions of temperature and pressure to promotedehydrogenation and disproportionation.

In the process disclosed in U.S. Pat. No. 3,445,541, thedisproportionation reaction is carried out using a catalyst whichcontains a known olefin disproportionation component such as tungstenoxide or molybdenum oxide. Group VIII noble metals are not conventionalolefin disproportionation components.

Numerous patents, including U.S. Pat. Nos. 3,437,709, 3,476,821 and3,281,483, have disclosed disproportionation using a crystallinealurninosilicate molecular sieve (molecular sieve) catalyst, such asmordenite. However, these prior art disclosures involvedisproportionation of alkyl aromatics such as toluene, notdisproportionation of alkanes.

U.S. Pat. No. 3,175,967 discloses at column 12, line 64, that H O bringsabout the deactivation of a molecular sieve catalyst used, for example,in cracking reactions. U.S. Pat. No. 3,437,709 discloses that in thedisproportionation of alkyl aromatics small amounts of oxygen supplyingmaterials, preferably air or oxygen, act to increase thedisproportionation of methyl-substituted aromatic compounds. Oxygensupplying materials other than the preferred air listed in U.S. Pat. No.3,437,709 are oxygen, C0 t-butanol, water, phenol, benzoic acid, benzylalcohol, and benzaldehyde. As mentioned above, U.S. Pat. No. 3,437,709relates to disproportionation of the alkyl aromatics and not todisproportionation of alkanes.

SUMMARY OF THE INVENTION According to the present invention, a processis provided for disproportionating feed light alkanes to obtain highermolecular weight hydrocarbons which comprises contacting a light alkane,at elevated temperature and pressure, with a catalyst comprising amolecular sieve composited with a Group VIII noble metal.

Crystalline alumino-silicate zeolites, commonly referred to as molecularsieves, are well known in the art. They are characterized by theirhighly ordered crystalline structure and uniformly dimensioned pores,and are distinguishable from each other on the basis of composition,crystal structure, adsorption properties and the like. The termmolecular sieves, is derived from the ability of these zeolite materialsto selectively absorb molecules on the basis of their size and form. Thevarious types of molecular sieves may be classified according to thesize of the molecules which will be rejected (i.e., not adsorbed) by aparticular sieve. U.S. Pat. Nos. 3,013,982-86 describe a number of thesesynthetic zeolites, designated therein as Zeolite A, D, L, R, S, T, Xand Y. In addition to their extensive use as adsorbents for hydrocarbonseparation processes and the like, it has recently been found thatcrystalline aluminosilicate zeolites, particularly after cation exchangeto reduce alkali metal oxide content, are valuable catalytic materialsfor various processes, particularly hydrocarbon conversion processes.

In general, the chemical formula of the anhydrous crystallinealuminosilicate zeolites expressed in terms of moles may be representedas:

0.9 i0.2M O:Al O XSiO wherein M is selected from the group consisting ofhydrogen, monovalent and divalent metal cations and mixtures thereof; nis its valence, and X is a number from about 1.5 to about 12, said valuebeing dependent upon the particular type of zeolite. The zeolite asproduced or found naturally normally contains an alkali metal such assodium or an alkaline earth metal such as calcium. Among the well-knownnatural zeolites are mordenite, faujasite, chabazite, gmelinite,analcite, erionite, etc. Such zeolites differ in structure, composition,and particularly in the ratio of silica to alumina contained in thecrystal lattice structure. Similarly, the various types of syntheticcrystalline zeolites, e.g., synthetic faujasite, mordenite, etc., willalso have varying silica to alumina ratios depending upon such variablesas composition of the crystallization mixture, reaction conditions, etc.For the synthetic faujasite type, X in the above formula has a value offrom about 2 to about 7, preferably 5.0 to 5.5; for the syntheticmordenite type, X has the value of from about 8 to about 12, preferably,9.5 to 10.5; and for the Zeolite A type, X has a value of about 1.5 toabout 5, preferably 1.9 to 3.

In the process of the present invention, the catalyst comprises amolecular sieve composited with a Group VIII noble metal and it isparticularly preferred to use mordenite as the specific molecular sieveportion of the catalyst. The noble metals which are used together withthe molecular sieve portion of the catalyst are Group VIII noble metals,sometimes referred to as the platinum group noble metals, andspecifically including .palladium, platinum, rhodium, ruthenium, osmiumand iridium. Particularly good results have been achieved in accordancewith the process of the present invention using palladium, and aparticularly preferred catalyst composite for use in the process of thepresent invention is palladium composited with mordenite.

It is preferred to carry out the contacting of the feed light alkanewith the catalyst at a pressure between 50 and 4,500 psig and atemperature between 700 and l,750 F. In the process of the presentinvention, it is particularly preferred to carry out the contacting ofthe feed light hydrocarbons with the catalyst at a temperature between950 and l,350 F.

The present invention is directed to the disproportionation of lightalkanes, i.e., saturated or paraffinic hydrocarbons which boil at arelatively low temperature such as propane, butanes, pentanes, andhexanes. Particularly preferred light hydrocarbons feedstocks arepropane, isobutane and normal butane. The process of the presentinvention has been found to give particularly advantageous results interms of produc tion of more valuable hydrocarbons when the process ofthe present invention is used to disproportionate a hydrocarbonfeedstock composed mostly of propane. The term mostly is used to connotethat the propane feedstock is at least 50 per- 5 cent propane.Preferably, the propane feedstock is at least 80-90 percent propane.

The process of the present invention can be carried out in the presenceof H 0 or substantially in the absence of H 0. However, it is preferredto have at least minor amounts of H 0 present during the contacting ofthe hydrocarbon feed with the catalyst. Because of the elevatedtemperature employed in the process of the present invention, usually HO will be present in the form of steam. Preferably H O is added to ormixed with the feed light alkanes immediately before the light alkanesare contacted with the molecular sieve Group VIII noble metal catalyst,It is preferred to use about 0.2 to 80 and more preferably 1.0 to 50volume percent H O based on the total volumetric amount of the H 0 andlight alkanes fed to the contacting step in the process of the presentinvention. The volumetric amounts of light alkanes and H 0 is based onvolumes calculated for these constituents at 60 F. and normalatmospheric pressure.

In the process of the present invention, it is believed that the H 0serves to reduce catalyst fouling and increase the yield of highermolecular weight hydrocarbons. It is not known exactly how the H 0functions in the process of the present invention, but we have obtaineddecreased fouling and plugging of small lines in laboratory equipmentwhen using H O together with the alkane feed to the high temperaturereactor, and surprisingly good yields of higher molecular weighthydrocarbons have been obtained in the laboratory when using H O withthe feed to the high temperature catalytic reaction.

More narrow preferred operating conditions for the process of thepresent invention include a temperature between l,000 and 1,300 F. and apressure between 1,000 and 3,000 psig. Two particularly preferredcatalysts for use in the process of the present invention are palladiumon mordenite and platinum on mordenite.

DETAILED DESCRIPTION In accordance with a very preferred embodiment ofthe present invention, a propane feedstock is disproportionated bycontacting the propane, in the presence of at least 0.5 volume percent H0 and at a temperature of about l,070 to 1,l90 F. and a pressure ofabout 750 to 300 psig, with a catalyst comprising palladium onmordenite. Preferably the LI-ISV is between 1.0 and 9.0, based on thecombined volumetric feed rate of H 0 and propane.

In one specific run (Run A) using the process of the present invention,propane was disproportionated to form higher and lower molecular weighthydrocarbons. The operating conditions for Run A were as follows:

A yield of over I 1 weight percent C hydrocarbons was obtained from therun at the conditions as specified above. Thus, a very substantialamount of heavy hydrocarbons are produced by disproportionating propanein a process in accordance with the present invention. Table I belowfurther summarizes the results obtained from Run A at the conditionsspecified above and also tabulates data on two further runs, B and C.

conversion.

TABLE I Weight percent yields Run A B C D Compound:

CH4 16. 5 Ethene 2. 3 Ethane. 8.5 Propane 1 60. 1 Isobutane 1. 3lsobutene 1. 2 N -Butane 1. 3 N-B utenes 6 0.3

8. 5 Aromatics in C5 3 .4 2. 9 Ultimate yield of useful" materia 38. 637. 1 23.6 37. 4 '1emp., F 1,132 1,130 1,144 1,018 LHSV (propane). 4. 4.0 4. 0 4. 0 LHSV H2 4. 0 4. 0 4. 0 0 LHSV total 8. 0 8.0 8. 0 4. 0

1 Probably some propylene in the propane. propylene was not split out onchromatograph used to analyze the product.

= Ethane plus butenes plus C X100=ultimate yield propane It can be seenfrom Table I that temperatures in the vicinity of 1,000 l,300 F. andpreferably temperatures above l,l00 F. should give attractive yields ofhigher molecular weight hydrocarbons in a process in accordance with thepresent invention. Particularly, temperatures in the range of about1,100 l,l60 F. give attractive yields of valuable hydrocarbons by adisproportionation process in accordance with the present invention.

Although various embodiments of the invention have been described, it isto be understood that they are meant to be illustrative only and notlimiting. Certain features may be changed without departing from thespirit or scope of the invention. It is apparent that the presentinvention has broad application to the disproportionation of lightalkanes in the presence of H 0 using a catalyst comprising a molecularsieve and a Group VIII noble metal. Accordingly, the invention is not tobe construed as limited to the specific embodiments or;

examples discussed but only as defined in the appended claims.

I claim:

1. A process for disproportionating feed light alkanes selected from thegroup consisting of propane, normal-butane and isobutane and mixturesthereof, which comprises contacting the light alkane, in a reactionzone, at a temperature between 1,000 and 1,300 F., with a catalystcomprising a molecular sieve composited with a metal selected from thegroup consisting of palladium, platinum, rhodium, ruthenium, osmium andiridium.

2. A process in accordance with claim 1 wherein the contacting iscarried out at a temperature between 1,l00 and 1,300 F.

3. A process in accordance with claim I wherein the molecular sieve ismordenite.

4. A process in accordance with claim 1 wherein the catalyst comprises amolecular sieve-composited with palladium or platinum.

5. A process in accordance with claim 1 wherein the reaction is carriedout in the presence of H 0.

6. A process in accordance with claim 1 wherein 0.5 to 50 volume percentH O, based on the volume of light alkane feed, is fed to the reactionzone.

7. A process in accordance with claim 1 wherein the catalyst comprisespalladium on mordenite.

8. A process for disproportionating propane to obtain higher molecularweight hydrocarbons, selected from the group consisting of alkane,olefin, and aromatics or aromatic mixtures thereof which comprisescontacting the propane, in the presence of about 0.5 to 50 volumepercent H 0 and at a temperature of about 1,070 to 1,190 F. and apressure of about 50 to 4,500 psig, with a catalyst comprising palladiumon mordenite.

2. A process in accordance with claim 1 wherein the contacting iscarried out at a temperature between 1,100* and 1,300* F.
 3. A processin accordance with claim 1 wherein the molecular sieve is mordenite. 4.A process in accordance with claim 1 wherein the catalyst comprises amolecular sieve composited with palladium or platinum.
 5. A process inaccordance with claim 1 wherein the reaction is carried oUt in thepresence of H2O.
 6. A process in accordance with claim 1 wherein 0.5 to50 volume percent H2O, based on the volume of light alkane feed, is fedto the reaction zone.
 7. A process in accordance with claim 1 whereinthe catalyst comprises palladium on mordenite.
 8. A process fordisproportionating propane to obtain higher molecular weighthydrocarbons, selected from the group consisting of alkane, olefin, andaromatics or aromatic mixtures thereof which comprises contacting thepropane, in the presence of about 0.5 to 50 volume percent H2O and at atemperature of about 1, 070* to 1,190* F. and a pressure of about 50 to4,500 psig, with a catalyst comprising palladium on mordenite.